r.'.M'i Transactions of the Society. 



steel cone D. The steel cone is itself hollow, and is closed by a 

 -mall metal cap L. A lead or steel weight K is fitted on to the 

 steel cone D, and is clamped in any desired position along it. The 

 apparatus is mounted on a cone H, and runs between this cone and 

 the centre I. It may conveniently be connected directly up to a 

 motor, as shown in the illustration, or may be driven by a belt 

 from any suitable source of power by putting a groove pulley on 

 the left hand end of the spindle. 



The grinding action takes place between the steel balls con- 

 tained in the metal vessel and the interior surface of the same. It 

 is evident that if the weight K were not on the central cone as 

 shown, or unless some similar method were adopted to control 

 the cone to prevent it from rotating, no grinding action would 

 result ; the central steel cone, in fact, must either remain still or 

 be allowed to rotate at a slower speed than the containing vessel. 

 The metal weight K is of such size that on the whole machine 

 being driven at a suitable speed the action of gravity results in the 

 steel cone remaining still and so a grinding action takes place 

 between the steel balls and the inside surface of the containing 

 vessel. 



To ensure that all the bacterial or other cells are as quickly as 

 possible brought under the grinding action of the balls, the speed 

 of rotation should be high. In practice it has been found that 

 from 1000 to 1500 revolutions per minute is a convenient speed, 

 and that centrifugal action is then sufficient to ensure that the 

 whole of the material does actually come between the balls and the 

 metal vessel. 



The method of using the machine is briefly as follows : The 

 bacteria after being removed from the culture tubes or plates on 

 which they are grown, are centrifugalized ; the semi-fluid mass is 

 then emulsified with saline solution, so that it is of a creamy con- 

 sistence. This material is then introduced into the container by 

 means of a pipette through the hollow centre of the steel cone. 

 This ensures that no parts of the machine are disturbed more than 

 is absolutely necessary either before or after grinding. The 

 machine is then run for a longer or shorter period depending on 

 the amount of material to be dealt with, and the ground material 

 is then pipetted off through the steel cone. As the balls are 

 themselves free to rotate, the amount of friction is negligible, but 

 any rise of temperature may be prevented by allowing a small 

 stream of carbonic acid gas from a cylinder of liquid carbonic acid 

 to impinge on to the side of the vessel ; alternatively an ether 

 spray, such as is used for section-cutting purposes, may be used, 

 and will be found quite efficient. 



The vertical type of machine (fig. 73) is exactly similar in all 

 essential details except that the central steel cone is controlled by 

 means of electro-magnets. On the top of the cone a mass of 



